1. Field of the Invention
An aspect of the present invention relates to a developing apparatus to be used in an image forming apparatus employing an electrophotographic system, such as a copying machine, a multifunction peripheral, a printer, or a facsimile machine, and to an image forming apparatus employing the developing apparatus.
2. Description of the Related Art
In a conventional image forming apparatus employing an electrophotographic system, the surface of an image bearing member is uniformly charged, and then image exposure is performed by using, for example, a semiconductor laser or a light-emitting diode (LED). An electrostatic latent image is formed on the image bearing member, and, then, this electrostatic latent image is turned into a toner image by a developing apparatus before transferring it onto a transfer material. As is known in the art, thereafter, the toner image is fixed to the transfer material by a fixing apparatus before outputting the transfer material.
In recent years, there has been an increasing demand for an improvement of image forming apparatuses in terms of speed and image quality. As a developing apparatus for use in such an image forming apparatus capable of high speed outputting, there is an image forming apparatus which is equipped with a plurality of developer carrying members carrying developer.
Apart from this, in order to achieve a reduction in the number of components, a known developing apparatus has the developer carrying members opposing each other in close proximity, with one developer carrying member regulating the developer carried by the other developer carrying member at the opposing position.
Further, in connection with the above-described developing apparatus, there has been proposed a developing apparatus including a first developer carrying member serving as a swinging center, a second developer carrying member swingable around the first developer carrying member while maintaining a predetermined gap, and four abutment rollers respectively provided at both ends of the first and second developer carrying members and consisting of circular members used to guarantee a gap between an image bearing member and the second developer carrying member, whereby, as compared with a construction utilizing no swinging movement, it is possible to secure the requisite gap between the image bearing member and the second developer carrying member in a more stable manner.
However, when such a swinging construction is adopted, it is rather difficult to fix a second magnetic field generating member, which is provided in the second developer carrying member that is swingable, to a container.
To deal with the above problem, there has been proposed a developing apparatus of the type which includes a first developer carrying member serving as a swinging center and a second developer carrying member swingable around the first developer carrying member, wherein a second magnetic field generating member is set in position with respect to a connecting member connecting the first developer carrying member and the second developer carrying member to each other, whereby it is possible to perform positioning of magnetic poles without hindering the swinging movement of the second developer carrying member as discussed in Japanese Patent Application Laid-Open No. 2009-116261.
However, when such a developing apparatus, in which one developer carrying member is swingable, is attached to the body of an image forming apparatus, variation occurs in component precision in terms of the angle by which the second developer carrying member swings.
Since the first magnetic field generating member is set in position with respect to a developing container, and the second magnetic field generating member is set in position with respect to the swinging connecting member, such variation in the angle by which the second developer carrying member swings results in variation in the relative positions (phase) in the peripheral direction of the (the peripheral direction of the first and second developer carrying members) first and second magnetic field generating members. That is because, when the connecting member swings, the second magnetic field generating member swings integrally therewith, whereas the first magnetic field generating member, which is fixed to the developing container, does not swing.
In particular, in the developing apparatus of the type in which one of the first and second developer carrying members regulates the developer carried by the other in the gap (hereinafter referred to as the SS-gap) across which the first and the second developer carrying members are opposed to each other, the phase of the opposing magnetic poles (hereinafter referred to as the SS-poles) of the first and second magnetic field generating members is of importance.
Thus, due to deviation in the phase of the SS-poles caused by the above-mentioned variation in the swinging angle of the second developer carrying member, there is a possibility of a defective coating of the surface of the developer carrying members, which may cause an image defect such as unevenness in density.